1. The Field of the Invention
The present invention relates generally to a subcutaneously implantable access port. More specifically, the present invention relates to an access port having a plurality of needle-penetrable, self-sealing septums, each affording repeated access to a corresponding plurality of distinct fluid cavities each in communication with a plural lumen catheter.
2. Background Art
A variety of implantable devices, known as subcutaneous access ports, are utilized to deliver fluids to or to withdraw fluids from the bloodstream of a patient.
Such access ports typically include a needle-impenetrable housing which encloses one or more fluid cavities and defines for each such fluid cavity an access aperture communicating through the housing on the side thereof which is adjacent to the skin of the patient when the access port is implanted in the body thereof.
A needle-penetrable septum is received in and seals each access aperture. Exit passageways located in an outlet stem communicate with each of the fluid cavities for dispensing medication therefrom to a predetermined location in the body of the patient through an implanted catheter attached to the access port.
Once the access port and the catheter have been implanted beneath the skin of a patient, quantities of medication or blood may be dispensed from one such fluid cavity by means of a non-coring needle passed through the skin of the patient and penetrating the septum into one of the respective fluid cavities. This medication is directed in the distal end of the catheter to an entry point into the venous system of the body of the patient.
Blood may also be withdrawn for sampling from the body of a patient through such an access port. This is accomplished by piercing the skin of the patient and one of the respective septums with a non-coring needle and applying negative pressure thereto. This causes blood to be drawn through the catheter into the fluid cavity corresponding to the pierced septum and then out of the body of the patient through the needle.
To prevent clotting thereafter, the withdrawal route is flushed with a saline solution or heparin using again a non-coring needle piercing the skin of the patient and the septum in the same manner as if a medication were being infused.
Both intermittent and continual injections of medication may be dispensed by the access port. Continual access involves the use of a non-coring needle attached to an ambulatory-type pump or a gravity feed IV bag suspended above the patient. The ambulatory-type pump or the IV bag continually feeds the medication or fluid through the needle to the fluid cavity in the access port and from there through the catheter to the entry point into the venous system.
To facilitate locating each respective septum once the access port has been implanted, some access ports incorporate a raised circular ring located about the entire outer perimeter of the septum. This raised ring enhances the tactile sensation afforded by the subcutaneous septum to the palpating fingertip of a medical practitioner.
One problem encountered with the use of a raised ring, however, is that tissue located within the area encircled by the ring does not receive a sufficient quantity of blood. This lack of adequate blood flow may lead to necrosis of the encircled tissue. Necrosis adversely affects the localized tissues, and interferes with the passage of a needle therethrough, as well as destabilizing the pocket in which the access port is implanted.
A related problem arises as a physician attempts to access the septum during use. While a physician may tactually locate the septum through the use of such a raised ring, the natural tendency to avoid missing the septum with the needle causes most physicians to direct the needle through the septum at a point near the raised ring. While the useful life of the self-sealing septum is usually over one thousand penetrations, this assumes that the penetration will be randomly distributed over the surface of the septum. In concentrating the needle punctures near the perimeter of the septum next to the raised ring, the useful life of the septum is dramatically reduced.
Although the raised ring allows a physician to determine the location of the septum by touch, the portion of the septum that can be positively identified is usually only the perimeter of the rubberized septum, which is typically circular. As a result, the location of one septum does not in any way indicate in which direction the second septum is located.
To preclude reaction with the tissues in the body of a patient, access ports are constructed of nonreactive materials, such as titanium or stainless steel. Although these materials are nonreactive, access ports constructed utilizing titanium or stainless steel materials produce an interfering or blurred image of the body of the patient in the vicinity of the implanted access port when diagnostic imaging techniques such as magnetic resonance imaging (hereinafter "MRI"), CAT scans, or computerized tomography are used. The blurred region caused by the presence of a metallic access port in the body of a patient extends beyond the access port itself. Therefore, the use of metallic access ports limits the diagnostic imaging techniques that may be used relative to those areas of the body in which an access port is implanted. In place of metallic materials some access ports have been fabricated at least in part from biocompatible plastics.
A further problem relating to the materials for and manufacture of access ports is the deleterious impact of some manufacturing procedures on the fluids which flow through the fluid cavities and related structures located between the fluid cavities and the catheter. During the manufacture of an access port, whether the port is comprised of metallic or plastic materials, it becomes necessary to form the fluid cavities and exit passageways through which the fluid will be directed into the attached catheter.
This manufacturing process often leaves sharp edges and corners in the areas where the fluid cavity is to direct the flow of the fluid through an exit passageway. As blood or other fluids are injected through the septum into the fluid cavity, pressure developed within the fluid cavity tends to cause fluid to flow through the exit passageway. As the fluid in the fluid cavity flows past the sharp edges and corners produced in a manufacture of the access port, turbulence arises, taking the form of a vortex, adjacent to the sharp edges and corners. Some fluids, such as blood, are sensitive to this turbulence, and lysing of the red blood cell component of the injected blood can occur in these turbulent areas.
In addition, the machining of the circular fluid cavities often results in the creation of areas within the housing in which fluid flow is retarded. These areas are referred to as dead spaces and usually occur in areas of transition, such as where the bottom of the septum interfaces with the walls of the fluid cavity and where the floor of the fluid cavity meets the exit passageway through which the fluid must flow. As the flow of fluids through dead spaces is retarded, stagnation occurs, resulting in some fluid being trapped within these dead spaces. If the access port is used to transfuse blood, blood trapped in these dead spaces may form clots and block the flow of fluid through the fluid cavity.
A further problem encountered in the design and construction of access port relates to the positioning of the septums within the housing of the access port. The positioning of the septums within the housing is a compromise between two conflicting objectives. These are the need to separate the septums to such a distance so that the septums may be easily differentiated for the purpose of injection and the need to restrict the overall dimensions of the access port, which must be placed within a tissue pocket of fairly small dimensions.
The distancing of the septums to facilitate their differentiation, however, results in a corresponding distancing of the fluid cavities. This result is at odds with another structural requirement for access ports with plural cavities, namely that the exit passageways from each fluid cavity be closely spaced at the point where the implanted catheter is to be coupled to the access port.
To guide the flow of a fluid from each of the spatially separated fluid cavities into the side-by-side configuration of fluid outflow necessitated by the dimensions of a plural lumen catheter, intermediate structural members have been required. Naturally, this complicates the process of manufacture and increases its cost, as well as the chances of structural failure.
There are several examples of such intermediate members used to resolve the manufacturing constraints imposed upon the construction of a passageway flowing from spatially separate fluid cavities into a side-by-side configuration acceptable by a catheter.
One is to produce passageways in the form of bent metal tubes which are then insert molded or welded into the larger body of the access port. The use of such a metal component will interfere with the production of an access port which is free of limits as to the diagnostic imaging techniques that may be used relative to those areas of the body in which an access port is implanted.
In addition, the non-integral nature of such metal outlet passageways raises the possibility of leakage of medication through the interstices between the metal tubes and the body of the access port.
Alternatively, to produce fluid flow from spatially separated fluid cavities into the closely spaced lumens of a catheter, each fluid cavity has been designed with its own spatially separated outlet stem. These outlet stems are then coupled by a hub structure for permanent attachment to the closely spaced lumens of a catheter. This type of arrangement increases the size of the overall access port and its cost of manufacture by adding thereto the necessity of fabricating and assembling the hub element.
Port connections to catheters in this manner are permanent. Accordingly, if the catheter is to be shortened by trimming that trimming must occur at the distal end of the catheter, and this precludes the use thereat of any type of specially designed tip or valve.
One additional set of problems encountered in the use of access ports relates to the actual connection of the catheter to the access port. This is most commonly effected by securing the catheter to an outlet stem protruding from the housing of the access port. In an attempt to lock the catheter to the outlet stem of the access port, thread-type systems have been developed wherein the catheter is attached to an outlet stem, and the outlet stem is then threaded into the access port. When utilizing this system, however, it is difficult to determine the amount of engagement of the catheter onto the outlet stem. Some catheter connection systems do not allow visual verification of attachment. As a result, leakage and failure can occur.
To overcome this problem, access ports are produced in which the catheter is pre-attached at the factory. While this practice alleviates many of the problems with leakage and failure due to catheter slippage, this system severely limits the type of the catheter usable with the access port. As mentioned above, this precludes the use of catheters having specialized distal tips, as the distal end of the catheter is the only end that can then be trimmed to effect its ultimate sizing. For example, catheters utilizing a Groshong.RTM. slit valve at their distal end may not have any of the distal tip of the catheter removed without compromising the catheter.